Anion exchange polymers comprising a perfluorinated backbone and pendant chains covalently bonded to the perfluorinated backbone comprising quaternary ammonium groups are known in the prior art.
EP 166015 A (TOYO SODA MANUFACTURING INC) Jan. 2, 1986 discloses ion exchange membranes comprising a fluorocarbon anion exchange polymer. The polymer is composed of a fluorocarbon polymer comprising a perfluorocarbon main chain and a pendant chain attached to the main chain, having a terminal group represented by the formula: —SO2N(R4)—(CH2)a—NR1R2R3Z, where R1 is a lower alkyl group, an aromatic group or an alkyl group containing quaternary ammonium group(s), R2 is a lower alkyl group, an aromatic group or a hydroxy-lower alkyl group, or R1 and R2 together form a tetramethylene or pentamethylene group, R3 is a lower alkyl group, R4 is a hydrogen atom, a lower alkyl group or an alkyl group containing quaternary ammonium group(s), a is an integer of 2 to 5, and Z is a counter ion for the quaternary ammonium ion. The membranes are obtained by reacting a fluorocarbon polymer comprising fluorosulfonyl terminal groups with an amine of formula HNR4—(CH2)a—NR1R2, where R1, R2, R4 and a are as defined above, followed by reaction with an alkylating agent to convert the tertiary amino group into a quaternary ammonium group.
EP 1612874 A (SOLVAY SA) Jan. 4, 2006 discloses anion exchange membranes comprising a support polymer and groups of formula —SO2NR1Q+ covalently bonded to the support polymer, wherein Q+ is a group comprising at least one quaternary nitrogen atom, and R1 is H or a C1-C20 alkyl group, or forms a ring together with a group in Q+, wherein the ring contains 2 to 10 carbon atoms and, optionally, up to 4 heteroatoms. The support polymer is in the form of a film. Examples of support polymers include fluorinated and perfluorinated polymers as well as non-fluorinated polymers. The membranes are obtained by reaction of a suitable amine with a support polymer comprising sulfonyl groups.
Liquid dispersions of fluorinated anion exchange polymers in organic solvents have been disclosed in JP 62-161866 A (TOYO SODA MANUFACTURING LTD) Jul. 17, 1987, which discloses liquid compositions comprising a mixed solvent comprising at least one solvent selected from dimethylformamide, dimethylsulfoxide, hexamethylphosphoric acid triamide and 1,3-dimethyl-2-imidazolidinone and 20 to 90 wt % of isopropanol and a fluorinated anion exchange polymer comprising a quaternary ammonium salt including the following:
wherein Z is selected from halogen, BF4, SbCl6, RSO3, RCOO, R being a lower alkyl or fluoroalkyl or a non-substituted phenyl group. The composition disclosed in the examples however contains low amounts of the fluorinated anion exchange polymer (2.7 wt %).
JP 62-161867 A (TOYO SODA MANUFACTURING LTD) Jul. 17, 1987 similarly discloses liquid compositions comprising the fluorinated anion exchange polymer comprising a quaternary ammonium salt described in JP 62-161866 and a three-component mixed solvent comprising at least one solvent selected from methanol and ethanol, isopropanol and water. No information is given concerning the concentration of the fluorinated anion exchange polymer achievable in the three-component liquid composition.
JP 2001-081261 A (ASAHI GLASS LTD) Mar. 27, 2001 discloses the preparation of fluorinated anion exchange polymers having quaternary ammonium ion exchange groups by reaction of a fluorinated polymer having —SO2F or —SO2Cl end groups with a diamine followed by reaction with e.g. an alkyl halide. Compositions comprising the anion exchange polymers in fluorinated alcohols (for instance hexafluoro 2-propanol) are described as well as their use for preparing ion exchange membranes. Concentrations of the anion exchange polymers in the fluorinated alcohol of about 2 wt % are disclosed in the examples
From the foregoing it appears that the need still exists for liquid compositions of fluorinated anion exchange polymers having quaternary ammonium ion exchange groups containing higher amounts of the polymer. However, it has now been found that in order to obtain a liquid composition containing at least 5 wt % of a fluorinated polymer having quaternary ammonium ion exchange groups liquid media comprising less than 25 wt % of an alcohol should be used. Liquid compositions containing at least 5 wt % of the anion exchange fluorinated polymer are particularly suitable for preparing films or membranes by casting, as lower concentrations of the polymer generally lead to the formation of thin films which lack the desired mechanical resistance for most applications.
Thus, a need still exists for liquid compositions comprising a fluorinated anion exchange polymer having an appropriate concentration of the fluorinated anion exchange polymer to be suitably employed for the preparation of films, membranes and electrode layers by casting or coating techniques.